FREQUENCY OF SONIC OCCURRENCES AT BHI 

 Four Hour Intervals 



2000 2000 2000 2000 2000 2000 



28 FEB. 61 6 MAR. 61 7 MAR. 61 13 MAR. 61 18 MAR. 61 19 MAR. 61 



24 Hours 24 Hours ^...^ 24 Hours 24 Hours 24 Hours 



TIME 



FIG. 18 



